The invention relates to an insertion device for inserting a subcutaneous device into body tissue, and to an insertion aid and a subcutaneous device for use in such an insertion device. Such insertion devices, subcutaneous devices and insertion aids are used in the field of medical diagnostics in particular, more particularly in the field of so-called home monitoring, more particularly for monitoring a concentration of at least one analyte in a bodily fluid, e.g. blood or interstitial fluid. However, other applications are also possible.
The field of medical diagnostics or therapy has disclosed subcutaneous devices, i.e. devices that are designed to be inserted, wholly or partly, into body tissue, e.g. interstitial fatty tissue. This introduction is also referred to as insertion or implantation. Examples of such subcutaneous devices can in particular be found in the field of diagnostics, more particularly in the field of long-term monitoring of subjects, for example within the scope of so-called “home monitoring” or else in a clinical context. Accordingly, the subcutaneous device can for example comprise at least one subcutaneous sensor, for example an electrochemical and/or optical sensor, for detecting at least one analyte in the body tissue and/or in a bodily fluid. Alternatively, or in addition thereto, the subcutaneous device may also comprise other types of medical devices, such as e.g. medication devices that can introduce specific active ingredients into the body tissue in a targeted and preferably dosed fashion. Without restricting further possible fields of application, embodiments incorporating the invention will substantially be described in the following text with reference to subcutaneous sensors.
Medical therapy or diagnostics often require that one or more physical and/or chemical parameters be detected in body tissue of a subject. Examples of such physical and/or chemical parameters are analyte concentrations of one or more analytes such as e.g. glucose. By way of example, a medical treatment, for example an administration of certain medicaments or a different embodiment of influencing the body or body functions of the subject, can be selected, depending on the detected parameters.
The prior art has disclosed a number of examples for, in particular, qualitative or quantitative detection of one or more analytes by implantable, subcutaneous sensors. Thus, the subcutaneous sensors may for example be based on electrochemical measurement principles and comprise one or more chemical substances (also referred to as “test chemicals” in the text below), which change one or more physically and/or chemically measurable properties if the at least one analyte to be detected is present. Examples of such test chemicals are test chemicals based on enzymes, which are used in e.g. electrochemical sensors. Other measurement principles are for example based on optical properties, in which at least one test chemical changes at least one optically detectable property if the at least one analyte to be detected is present. Reference can be made to all measurement principles within the scope of the present invention.
A technical and medical challenge consists of implanting (inserting) the subcutaneous device into the body tissue. Carrying out this insertion should cause as little pain as possible and it should be possible to place the subcutaneous device such that the latter can also remain, at least in part, in the body tissue for a relatively long period of time of e.g. a few hours up to a few days, and can for example supply measurement data. Therefore, the prior art has disclosed a number of insertion devices that, in addition to the subcutaneous device to be implanted, comprise one or more insertion aids. By way of example, such insertion aids may be wholly or partly embodied as insertion needles, for example in the form of cannulae, into which the subcutaneous device can be introduced or onto which the subcutaneous device can be applied in order to be implanted into the body tissue therewith. The insertion aid can subsequently be removed again, with the subcutaneous device at least partly remaining in the body tissue. In the process, part of the subcutaneous device may project out of the body tissue, for example for a later removal of the subcutaneous device.
The prior art often teaches introducing an elongate, subcutaneous sensor partly under the skin, for example with an insertion depth of between 10 and 20 mm, using a minimally invasive technique by means of a hollow needle. By way of example, this may be brought about perpendicularly or at an angle, for example at 45°. The skin of the subject is penetrated in the process. The hollow needle can once again be removed after the insertion and the sensor may remain in the skin or the tissue and be connected to an evaluation instrument, which e.g. is worn externally. Compared to their longitudinal extent, sensors are generally narrow in their width and thickness and are weak as a result thereof. Skin and tissue prevent the sensor from penetrating into the body tissue. In order to stabilize the sensor during the insertion, the latter should therefore be stabilized at times for the procedure as per the prior art. In the described prior art, this is generally brought about by the insertion aid as a separate auxiliary means, wherein the insertion aid for example is produced from steel, more particularly in the shape of a needle. The sensor must be held so that the sensor remains in the skin, even when the insertion needle is withdrawn. Since the sensor generally has a thickened holding and/or sensor contact region, which must likewise be removed from the insertion needle, the insertion needle generally has a slit design. The hollow needle formed thus may for example have a U-profile or an almost closed O-profile, or else an angular profile.
The insertion needle has in many cases been provided with a cutting edge at the front end for painless penetration of the skin and the body tissue. The needle shape of the insertion needle ensures that the force exerted by the body tissue onto the sensor front does not bring the sensor out of its stretched shape during the insertion of the sensor. The needle slit of the insertion needle to this end preferably has a narrower design than the sensor width; however, this requires a tapering in the sensor shaft region during the withdrawal and separation of the insertion needle from the sensor. It is alternatively possible for the needle slit to be arranged laterally (with respect to the flat sensor structure) on the insertion needle, with the width of the sensor significantly exceeding the sensor thickness. Here, the holding and contact region may protrude from the needle slit.
A technical challenge lies in releasing the sensor when the insertion needle is withdrawn. This can also be brought about by means of so-called “peel needles”. Such peel needles may for example comprise a metal film rolled up to form a solid tube, which opens when the sensor projecting from the alignment is withdrawn and is resealed thereafter.
In principle, as an alternative to using an insertion needle, it is also possible to introduce a relatively flexible sensor under the skin without such an insertion aid. An option for such an insertion consists of using high insertion speeds. However, such applications are in principle disadvantageous because the insertion is as a rule afflicted with high uncertainty and because there is for example the risk of damaging the sensor during the insertion. Moreover, a mechanically complex apparatus is generally required.
Alternatively, or in addition thereto, use can also be made of sensor elements that have a locally increased rigidity. Thus, U.S. Publication No. 2006/0015024 A1 for example describes a transcutaneous medical element which has a distal section with a more flexible design than a more rigid proximal section that penetrates the skin surface. However, a disadvantage of such sensor elements is that the more rigid, proximal section also remains in the body tissue after the insertion, which may cause injury in the body tissue and increased infliction of pain.
The prior art generally describes different types of insertion devices and insertion aids in detail. Thus, European Patent No. EP 0 678 308 B1 for example discloses an insertion principle, in which a flexible feeler can be implanted into body tissue by means of a hollow insertion needle and an attachment foot. The insertion needle has a slit running along one side so that the insertion needle can be withdrawn from the feeler.
German Patent No. DE 103 06 013 A1 and U.S. Publication No. 2006/0030824 have disclosed a temperature-sensitive cannula for introduction into body tissue. The cannula is flexible in an introduced state, and has a rigid state below a critical temperature range and a flexible state above the critical temperature range. Prior to the introduction of the cannula into the body tissue, the former is cooled to a temperature below the critical temperature range by cooling and is thereby made more rigid. Hence the cannula is stiffened before the penetration, while the material may soften after the penetration.
German Publication No. DE 10 2004 002 472 B4 and U.S. Publication No. 2007/0016149 have disclosed a puncturing needle for introducing a product into the human or animal body. The puncturing needle has a distal needle section and a proximal needle section with different materials, wherein the distal needle section is more flexible than the proximal needle section.
German Patent No. DE 101 17 286 A1, U.S. Publication No. 2004/0158230 and U.S. Publication No. 2008/0033399 have disclosed a soft cannula, which has increasing resilience during the application. Prior to the application, the cannula has at least one material with adjustable hardness or at least two materials with different hardnesses, with the material of greater hardness being released during the application. Thus, the material changes its hardness properties during the application, which can mainly be traced back to the composition of the cannula.
PCT Publication No. WO 03/080169 A1 has disclosed an insertion needle, which has a needle body and a distal end section, for inserting a subcutaneous device. The distal end section has a tip. Furthermore, the needle body has a longitudinal depression that is designed for at least in part holding a subcutaneous device. By way of example, the subcutaneous device can be held on the needle body by means of one or more rigidly designed grippers such that although said subcutaneous device is held during the insertion, it can be pushed off the insertion needle when the insertion needle is pulled out of the body tissue.
The known insertion devices and insertion aids in principle have a few technical disadvantages, which must be accepted or must be overcome in a complex fashion. Thus, the generally flexible sensor shaft must, by means of the needle shape of the insertion needle, be prevented from deviating laterally during e.g. the insertion using an insertion needle. In general, in order to remove the insertion needle, the sensor must, in the process, deviate from the alignment between a front, distal part (sensor tip) and a rear, proximal part (contact piece and/or holder) or the insertion aid must be brought out of this line by means of its movement. By way of example, this problem is explained in detail in European Patent No. EP 0 678 308 B1. Both require a significant amount of mechanical complexity, such as e.g. the complicated design of the sensor, insertion needle and/or insertion needle and sensor guide at a defined angle or along a circular path. The dynamic insertion method illustrated above is also generally connected to significant mechanical complexity.
A further disadvantage of known insertion devices and insertion aids consists of the fact that hollow needles generally have a significantly larger cross section than simple needles. Accordingly, the skin is penetrated by a significantly larger cross section than the actual sensor profile, which can lead to increased levels of pain being felt and to increased tissue destruction.
A further disadvantage of known insertion devices and insertion aids lies in the reliability of the insertion, namely, that it is not always possible to ensure that the sensor does not slip relative to the insertion needle during the insertion of the insertion needle into the body tissue. On the other hand, it is not always reliably possible to ensure that the sensor remains in the body tissue and is not removed again from the body tissue together with the insertion needle when the insertion needle is removed from the body tissue.